Determination of volatile biogenic amines in muscle food products by ion mobility spectrometry

The extent of spoilage of muscle food products was determined through measurement of volatile biogenic amines that emanated from food samples. The release of the amines was enhanced by addition of a few drops of an alkaline solution and the amines were monitored by ion mobility spectrometry (IMS). The limit of detection of the method for trimethylamine (TMA) was 2 ng and the measurement was completed within <2 min with short and long term reproducibility of 15 and 25%, respectively, for replicate samples. The method provides qualitative information as it distinguishes between different amines, as well as quantitative data for the key compounds. A good correlation was found between the IMS results and the microorganism populations in microbiological cultures. The effects of storage time and temperature and of the type of meat on the formation of biogenic amines were examined, and as expected, the higher the storage temperature the faster the spoilage. Thus, this pilot study shows that the measurement of biogenic amines can serve as an indicator for food spoilage or freshness.     

Characterization of volatile metabolites formed by molds on barley by mass and ion mobility spectrometry

The contamination of barley by molds on the field or in storage leads to the spoilage of grain and the production of mycotoxins, which causes major economic losses in malting facilities and breweries. Therefore, on‐site detection of hidden fungus contaminations in grain storages based on the detection of volatile marker compounds is of high interest. In this work, the volatile metabolites of 10 different fungus species are identified by gas chromatography (GC) combined with two complementary mass spectrometric methods, namely, electron impact (EI) and chemical ionization at atmospheric pressure (APCI)‐mass spectrometry (MS). The APCI source utilizes soft X‐radiation, which enables the selective protonation of the volatile metabolites largely without side reactions. Nearly 80 volatile or semivolatile compounds from different substance classes, namely, alcohols, aldehydes, ketones, carboxylic acids, esters, substituted aromatic compounds, alkenes, terpenes, oxidized terpenes, sesquiterpenes, and oxidized sesquiterpenes, could be identified. The profiles of volatile and semivolatile metabolites of the different fungus species are characteristic of them and allow their safe differentiation. The application of the same GC parameters and APCI source allows a simple method transfer from MS to ion mobility spectrometry (IMS), which permits on‐site analyses of grain stores. Characterization of IMS yields limits of detection very similar to those of APCI‐MS. Accordingly, more than 90% of the volatile metabolites found by APCI‐MS were also detected in IMS. In addition to different fungus genera, different species of one fungus genus could also be differentiated by GC‐IMS.     

Detection of explosives by ion mobility spectrometry

Ion mobility spectrometry is an effective method for detecting mine-explosive devices and explosive charges and for revealing objects and peoples who came into contact with explosives. This is because of the excellent analytical and performance characteristics of the corresponding instruments. In the present work, we described the objects to be detected, formulated the basic terms and definitions, considered the physicochemical basics of the separation of ions by their mobility in a gas under an electric field, and presented experimental data on the main analytical characteristics of spectrometers: their ability to identify analytes, resolution power, time to provide readings, sensitivity, and detection limit.     

Detection of perfluorocarbons using ion mobility spectrometry

An ISAS custom-designed ion mobility spectrometer equipped with a ionization source is used for the sensitive detection of traces of perfluorocarbons (PFCs, C₅F₁₂ to C₉F₂₀) in air, a class of substances for which a growing interest for industrial and environmental applications arose within the last years. Mobility spectra of the PFCs are presented, compared and discussed with regard to the possibility of identifying these analytes; detection limits are determined to be in the upper ng l⁻¹ range. Using a specific PFC as an example, a way to prevent unwanted contributions of non-product ions, the difference mobility spectrum, is introduced and described. Advantages and possibilities of this technique are briefly discussed.     

Monte Carlo simulation of ion transport in ion mobility spectrometry

A program for simulation of ion trajectories in ion mobility spectrometry (IMS) instruments has been developed and incorporated into SIMION 7.0 [Int. J. Mass Spectrom. 200 (2000) 3–25]. Simulations were based on elastic collisions between ions and gas particles and conducted for an IMS drift tube. The program was validated by comparing the reduced mobility of helium ions derived from the simulation with the experimental data for helium ions in neon drift gas in low electric fields. Typical IMS parameters, including pressure, temperature, and flow rate of the drift gas were taken into account in the simulations. The program demonstrates capabilities of generating IMS spectra and predicting ion transport efficiency and separating ions. For the IMS drift tube studied, a correlation between imperfection of the electric field distribution and low resolution has been observed.     

Direct differentiation of herbal medicine for volatile components by a multicapillary column with ion mobility spectrometry method

In this work, a headspace system coupled to a gas chromatographic column and ion mobility spectrometry was applied as a screening system to differentiate the crude and processed “atractylodis macrocephalae rhizoma” samples. The obtained ion mobility data were consecutively processed by principal component analysis and Radar fingerprint chart methods. From the principal component analysis for the initial solution to original variables, the two principal components accounted for 68 and 13% of the total variance, respectively. The established method was proven to be valuable for classification, discrimination between herbal medicines from different processing procedures.     

Evaluating the variation of ion energy under different parameter settings in traveling wave ion mobility mass spectrometry

Ion mobility mass spectrometry (IM-MS) can be used to differentiate and identify isobaric ions. To improve IM-MS resolution, the second generation of traveling wave ion mobility (TWIM) technology was launched. There were reports showing ions were heated up by TWIM. With higher ion energy, it could alter the conformation of larger ions or MS/MS experiments. To monitor the energy exchange relating to the TWIM process, the combined use of thermometer ions with unique molecular structure and theoretical calculations to determine the effective temperature of ions had been explored. In this report, the use of a simple experimental approach to estimate the variation on the ion energy that result from changing a TWIM parameter setting is demonstrated. The approach aims to achieve the same percentage of ion dissociation in a collision cell, which is part of the original instrument and located at the exit of TWIM cell. Similar to the traditional MS/MS experiments, the same level of ion dissociation could be achieved by adjusting the electrical potential that was applied to the collision cell. The higher the ion energy after the TWIM separation, the lower the electrical potential was required to achieve the same level of ion dissociation. Together with the information on the number of electrical charge in the selected ion, the difference in the required electrical potentials could be converted into electron volt of ion energy that resulted from changing the TWIM parameter setting. The results showed ion energy could be changed 1–9 eV when the parameter of TWIM was adjusted.     

Fingerprint identification of volatile organic compounds in gasoline contaminated groundwater using gas chromatography differential ion mobility spectrometry

Groundwater can be contaminated when e.g. gasoline tanks leak. Due to sampling and lab analysis, groundwater monitoring is time consuming and expensive. The technologies developed for rapid on-site analysis of gasoline contaminated groundwater face the technical limitation to distinguish the gasoline from complex matrices. In the present study the fingerprint identification of volatile organic components (VOCs) in gasoline contaminated groundwater using gas chromatography (GC) differential ion mobility spectrometry (DMS) is investigated. Groundwater was spiked with five sorts of gasoline (one reformulated gasoline, gasoline without additives and three different brand gasoline collected on petrol stations) and analyzed by GC-DMS. Seven VOCs (benzene, toluene, ethyl benzene, m-xylene, p-xylene, o-xylene, 1,2,4-trimethylbenzene) were identified by GC mass spectrometry (GC-MS) as well as by GC-DMS and selected as markers. The semi-quantitative determination of the selected compounds was achieved. The limits of detection of the GC-DMS are 46.42?ng for benzene, 1.13?ng for toluene, 1.80?ng for ethylbenzene, 0.22?ng for m-xylene, 1.13?ng for p-xylene, 0.61?ng for o-xylene and 0.37?ng for 1,2,4-trimethylbenzene, respectively. These results reveal the feasibility of GC-DMS for on-site monitoring of contaminated groundwater.     

Table of reduced mobility values from ambient pressure ion mobility spectrometry

This review presents a list of reduced ion mobilities that have been measured under ambient pressure conditions and reported in the open literature during the 16-year period of 1970-1985. Ions reported are listed in order of increasing reduced mobility along with the name of the parent compound, the reduced mobility of additional product ions observed in the spectrum, the carrier and drift gases, the temperature of the drift region and the reference where the data were reported. Also, ions that have been identified by mass spectrometry are indicated with an asterisk.     

Application of ion mobility spectrometry in study of surfactants adsorbed on different dish surfaces

Sodium lauryl sulfate (SLS) and sodium lauryl ether sulfate (SLES) are commonly used in many dishwashing liquids. These chemicals are adsorbed on the dish surface during the washing process and then transferred to food or drink in the cooking process. In this work, the adsorption of SLS and SLES on different dish surfaces in aqueous solution was studied. Stainless steel, copper, aluminum, Pyrex, Teflon and arcopal china ware were used in this study. The adsorbed chemical remained on the surface after rinsing was measured by thermal desorption using an ion mobility spectrometer as the detector. Although arcopal china ware showed the maximum amount of adsorption, and Pyrex and stainless steel dishes showed the minimum amount of residual chemical, the results showed that the amount of adsorbed chemicals on dish surfaces is less than 428 ng.cm^?2, which is well below the health risk dosage. The released SLS and SLES from dish surfaces into cold or hot water were also measured and compared for different dishes.     

Rapid preseparation of interferences for ion mobility spectrometry

Two new approaches to reduce false positive interferences commonly observed with explosives and drugs detection in the field were reported for ion mobility spectrometry (IMS). One of the approaches involved the rapid preseparation of potential interferences prior to detection by IMS. Firstly, it was found that the introduction of a short column packed with adsorption packing material before an IMS could help to reduce the false positive rates. Secondly, the retention time at which the most intense response occurred over the analysis time period could be utilized to separate false positive responses from target analytes with the same drift times. Rapid preseparation of potential interferences provided a greater degree of confidence for the detection (in less than 30 s) of drugs, explosives and chemical warfare agents (CWAs). Detection limits as low as 10 pg of TNT with a sensitivity of 12 A g⁻¹ were reported. Successful development of this technique may lead to the construction of a simple interface fitted with a short column of adsorption packing material to enhance either initial separation or to hold-back interferences mixed with explosive and drug responses in the field.     

Separation of amino acids by ion mobility spectrometry

The mobilities of the 20 common amino acids were determined by electrospray ionization ion mobility spectrometry. It was found that each amino acid had a different drift time and hence a different reduced mobility constant K0. This difference in drift time was less than 0.1 ms in many cases. With the instrument used in this study it would not be possible to resolve mixtures of some of the amino acids. It would however be possible to determine any single amino acid. In addition, the detection limits were determined for the 20 amino acids. They ranged from 50 to 700 pg. This indicates that the detection limits were less than 3 pmol for all of the amino acids and that many amino acids had detection limits less than 1 pmol.     

Using probabilistic relational learning to support bronchial carcinoma diagnosis based on ion mobility spectrometry

Ion Mobility Spectrometry (IMS) provides a means for analyzing the substances a person exhales. In this paper, we report on an approach to support early diagnosis of bronchial carcinoma based on such IMS measurements. Given the peaks in a set of ion mobility spectra, we first cluster these peaks with a modified k-means algorithm. We then apply probabilistic relational modelling and learning methods to a logical representation of the data obtained from the ion mobility spectra and the peak clusters. Markov Logic Networks and the MLN system Alchemy are employed for various modelling and learning scenarios. These scenarios are evaluated with respect to ease of use, classification accuracy, and knowledge representation aspects.     

Analysis of the volatile chemical markers of explosives using novel solid phase microextraction coupled to ion mobility spectrometry

Ion mobility spectrometry (IMS) is routinely used in screening checkpoints for the detection of explosives and illicit drugs but it mainly relies on the capture of particles on a swab surface for the detection. Solid phase microextraction (SPME) has been coupled to IMS for the preconcentration of explosives and their volatile chemical markers and, although it has improved the LODs over a standalone IMS, it is limited to sampling in small vessels by the fiber geometry. Novel planar geometry SPME devices coated with PDMS and sol-gel PDMS that do not require an additional interface to IMS are now reported for the first time. The explosive, 2,4,6-trinitrotoluene (TNT), is sampled with the planar SPME reaching extraction equilibrium faster than with fiber SPME, concentrating detectable levels of TNT in a matter of minutes. The surface area, capacity, extraction efficiency, and LODs are also improved over fiber SPME allowing for sampling in larger volumes. The volatile chemical markers, 2,4-dinitrotoluene, cyclohexanone, and the taggant 4-nitrotoluene have also been successfully extracted by planar SPME and detected by IMS at mass loadings below 1 ng of extracted analyte on the planar device for TNT, for example.     

Evaluation of micro-electrospray ionization with ion mobility spectrometry/mass spectrometry

In recent years, the resolving power of ion mobility instruments has been increased significantly, enabling ion mobility spectrometry (IMS) to be utilized as an analytical separation technique for complex mixtures. In theory, decreasing the drift tube temperature results in increased resolution due to decreased ion diffusion. However, the heat requirements for complete ion desolvation with electrospray ionization (ESI) have limited the reduction of temperatures in atmospheric pressure ion mobility instruments. Micro-electrospray conditions were investigated in this study to enable more efficient droplet formation and ionization with the objective of reducing drift tube temperatures and increasing IMS resolution. For small molecules (peptides), the drift tube temperature was reduced to ambient temperature with good resolution by employing reduced capillary diameters and flow rates. By employing micro-spray conditions, experimental resolution values approaching theoretically predicted resolution were achieved over a wide temperature range (30 to 250 °C). The historical heat requirements of atmospheric pressure IMS due to ESI desolvation were eliminated due to the use of micro-spray conditions and the high-resolution IMS spectra of GLY-HIS-LYS was obtained at ambient temperature. The desolvation of proteins (cytochrome c) was found to achieve optimal resolution at temperatures greater than 125 °C. This is significantly improved from earlier IMS studies that required drift tube temperatures of 250°C for protein desolvation.     

Detection of volatile organic compounds from wood-based panels by gas chromatography-field asymmetric ion mobility spectrometry (GC-FAIMS)

The focus of this work was to detect formaldehyde (HCHO) as a very volatile compound (VVOC) among other volatile organic compounds in the low concentration ranges that are relevant for the production control in wood processing industries. We show that a quick and easy derivatization of HCHO can be used for a reliable and straightforward identification with GC-FAIMS. Headspace samples of specimens made from wood-based panels were collected and pre-concentrated on a conventional solid phase microextraction fiber (SPME) and thermally desorbed in a split/splitless GC-injector. A standard gas-mixer generator based on the dynamical permeation principle was used to produce known concentrations of HCHO. The results are compared with gas chromatography??mass spectrometry (GC-MS).     

Identification of volatile chemical signatures from plastic explosives by SPME-GC/MS and detection by ion mobility spectrometry

This study demonstrates the use of solid-phase microextraction (SPME) to extract and pre-concentrate volatile signatures from static air above plastic explosive samples followed by detection using ion mobility spectrometry (IMS) optimized to detect the volatile, non-energetic components rather than the energetic materials. Currently, sample collection for detection by commercial IMS analyzers is conducted through swiping of suspected surfaces for explosive particles and vapor sampling. The first method is not suitable for sampling inside large volume areas, and the latter method is not effective because the low vapor pressure of some explosives such as RDX and PETN make them not readily available in the air for headspace sampling under ambient conditions. For the first time, headspace sampling and detection of Detasheet, Semtex H, and C-4 is reported using SPME-IMS operating under one universal setting with limits of detection ranging from 1.5 to 2.5 ng for the target volatile signatures. The target signature compounds n-butyl acetate and the taggant DMNB are associated with untagged and tagged Detasheet explosives, respectively. Cyclohexanone and DMNB are associated with tagged C-4 explosives. DMNB is associated with tagged Semtex H explosives. Within 10 to 60 s of sampling, the headspace inside a glass vial containing 1 g of explosive, more than 20 ng of the target signatures can be extracted by the SPME fiber followed by IMS detection.     

Monte Carlo simulation of ion transport in non-linear ion mobility spectrometry

A program for Monte Carlo simulation of ion transport in non-linear ion mobility spectrometry, also known as field asymmetric ion mobility spectrometry (FAIMS) or differential mobility spectrometry (DMS), has been developed. Simulations are based on elastic collisions between the ions and the gas particles, and take into account the effects of flow dynamics and asymmetric electric fields. Using this program, the separation and diffusion of the ions moving in a planar DMS filtration gap are demonstrated. Ion focusing in a cylindrical filtration gap is also confirmed. A characteristic compensation voltage is found to provide insight for understanding separation in non-linear ion mobility spectrometry. The simulation program is used to study the characteristics of non-linear ion mobility spectrometry, the effect of the carrier gas flow, and the dependence of the compensation voltage and nonlinear mobility coefficient (α) on the applied asymmetric electric field.     

Characterizing ion mobility and collision cross section of fatty acids using electrospray ion mobility mass spectrometry

This study investigated the ion mobility (IM) and the collision cross section (CCS) of fatty acids (FAs) using electrospray IM MS. The IM analysis of 18 FA ions showed intriguing differences among the saturated FAs, monounsaturated FAs, multi‐unsaturated FAs, and cis‐isomer/trans‐isomer with respect to the aliphatic tail chains. The length of aliphatic tail chain present in the ion structures had a strong influence on the differentiation of drift, while the number of double bond showed a weaker influence. The tiny drift differences between cis‐isomer and trans‐isomer were also observed. In the CCS measurements, two internal standards were involved in the mobility calibration and accuracy estimation. It insured our empirical CCS values were of high experimental precision (±0.35% or better) and accuracy (±0.25% or better). Moreover, the mass‐to‐charge ratio (m/z) – mobility plots obtained by ion mobility spectrometry with mass spectrometry analysis of FAs – was used to investigate the structural relationship between the molecules. Each series of FAs sharing a similar structure was aligned in the linear plot. Finally, the developed procedure was applied to the determination of FAs in rat adipose tissues, and it allowed the presence of 13 FAs to be confirmed with their exact masses and CCS values. These studies reveal the direct relationship between the behaviors in IM and the molecular structures and thus may provide further validations to the FA identification process. Copyright © 2015 John Wiley & Sons, Ltd.